In 1926, Huff left the company, and it was soon purchased by Hayden, Stone & Co., who increased capital to $1 million (United States) and renamed it Keystone.

Also in 1929, the Keystone–Loening plant on the East River in New York City was closed by Curtiss-Wright and the operation was moved to the Bristol, Pennsylvania.

The Keystone entry was for an all metal low winged monoplane bomber with retractable landing gear.

With a crew of 5 it was armed with up to 3 x .30 caliber machine guns and could carry 2,000 lbs (907 kg) of bombs on external racks.

A mock-up of the aircraft was inspected by the Air Corps in April and was withdrawn by Keystone after it was determined it could not meet the requirements.